Need help interpreting my first frequency measurements

[johnsen88]

Lads, with the suggestions of some members here, I got myself a UMIK mic and REW software. I have watched a couple of videos on how to get around measuring my speakers' frequency response. I have gone on to do this mainly to determine the extent of damage done to my drivers from an amplifier failure. The mid-bass drivers(the one in the Left speaker is more pronounced) produce a scratchy, distorted sound when recordings with instruments like double bass or cello are played. After what happened, the tweeter and the woofer sounded normal, but the ears could only pick up so much. The good lads here suggested that I pick up a mic and get some measurements done to determine where things stand and I have done so. Kindly excuse me for not being able to be more precise with the technical details. This is my very first attempt. I am no Amir or Erin(learnt so much from these two top fellas). I would appreciate it if you good people could interpret my findings and/or guide me on what I should have done. FYI, I have two new mid-bass drivers coming in this week to replace the damaged ones. Here are the two graphs. If there is anything I have missed out, please let me know.

Speakers: Focal Chorus 816v

Specs:

• 2 1/2 way: 16.5cm woofer; 16.5cm mid-bass; 25mm inverted dome tweeter
• 91.5dB Sensitivity
• 8 ohm impedance
• 47Hz - 28KHz frequency response

Test setup:

Mic was set up, pointed straight at the centre of the speaker's tweeter. The distance between the tweeter and the tip of the mic was 1m. I did a grille ON and grille OFF measurement but since I listen with the grilles OFF, I have included only those measurements. I can take further measurements if needed.

 

[ZolaIII]

Do the measurements from listening spot, use 90° angle and call file for it. Zipp the result and post it.

 

[staticV3]

Do you want to measure raw driver response?
Then do gated Ultra Nearfield measurements:
https://www.minidsp.com/applications/acoustic-measurements/loudspeaker-measurements

Do you want to measure the in-room frequency response?
Then use MMM at your main listening position:
https://www.audiosciencereview.com/...phone-method-mmm-for-dummies-using-rew.51333/

 

[Heinrich]

Lads, with the suggestions of some members here, I get myself a UMIK mic and REW software.

Congratulation for getting these high end devices! They're going to transform your listening experience, once the other stuff is adopted and corrected to what they say, granted.
The response shows a bit of trebble exaggeration, and weak low bass. The wiggles are normal. Some more advanced technique, 'gating', will get rid of them.

On the scratchy damage, you may want to perform a distortion test run. That points to the frequency range where it happens, and then after you could give a sine (hearing protection recommended, strongly) to the speaker and look for the overtone spectrum.

 

[johnsen88]

Do the measurements from listening spot, use 90° angle and call file for it. Zipp the result and post it.

Yes sir, I will do this later today. Thank you.

Do you want to measure raw driver response?
Then do gated Ultra Nearfield measurements:
https://www.minidsp.com/applications/acoustic-measurements/loudspeaker-measurements

Do you want to measure the in-room frequency response?
Then use MMM at your main listening position:
https://www.audiosciencereview.com/...phone-method-mmm-for-dummies-using-rew.51333/

I aim to obtain the driver response for both the mid-bass drivers. I want to confirm if the raspy, scratchy sound that is coming from these drivers is correctly identified and if the other drivers are working as they should. I don't have a reference frequency response graph to compare my readings. Focal did not publish any and they are reluctant to provide it.

 

[johnsen88]

Congratulation for getting these high end devices! They're going to transform your listening experience, once the other stuff is adopted and corrected to what they say, granted.
The response shows a bit of trebble exaggeration, and weak low bass. The wiggles are normal. Some more advanced technique, 'gating', will get rid of them.

On the scratchy damage, you may want to perform a distortion test run. That points to the frequency range where it happens, and then after you could give a sine (hearing protection recommended, strongly) to the speaker and look for the overtone spectrum.

Thank you! I wanted to maximise the setup I have and it is very reassuring to hear that these devices will be of immense help. I am still learning. I will be reading up more before I perform these tests. Just wanted to know if I am on the correct path in replacing both the scratchy drivers with new ones. Btw, does the graph reflect these findings?

 

[ZolaIII]

Which Focal's? For what you want you need to get out on the open ground and put them high... Just do the single measurement from listening spot and provide placement picture and room dimensions.

 

[johnsen88]

Which Focal's? For what you want you need to get out on the open ground and put them high... Just do the single measurement from listening spot and provide placement picture and room dimensions.

Focal Chorus 816v. Unfortunately, I live in an apartment and don't have access to an open space. However, I can do a single measurement from the listening point. Should the mic be at ear level?

Also, must I adjust any of the measurement parameters for this? Thank you.

 

[Heinrich]

Thank you! I wanted to maximise the setup I have and it is very reassuring to hear that these devices will be of immense help. I am still learning. I will be reading up more before I perform these tests. Just wanted to know if I am on the correct path in replacing both the scratchy drivers with new ones. Btw, does the graph reflect these findings?

First: please wear hearing protection, the noises are nasty for the hearing as they focus ALL THE ENERGY to a few hearing cells.

You're going to face two problems basically.

- Are the drivers really damaged?
Look out for the "distortion" tab in REW. The graphs you presented do not show.

- Are the new drivers working properly?
Compare frequency response old versus new. If there's a dip around 2kHz the polarity +/- wire is flipped (don't worry, happens all the time, I stll get nervous after many years of tinkering, it's costly stuff).

Focal Chorus 816v. Unfortunately, I live in an apartment and don't have access to an open space. However, I can do a single measurement from the listening point. Should the mic be at ear level?

Also, must I adjust any of the measurement parameters for this? Thank you.

That comes later, I suggest to repair first, right?

 

[ZolaIII]

Focal Chorus 816v. Unfortunately, I live in an apartment and don't have access to an open space. However, I can do a single measurement from the listening point. Should the mic be at ear level?

Also, must I adjust any of the measurement parameters for this? Thank you.

Yes central listening spot mic representing your head. You need to use cal(vibration) file for the angle which you obtain from manufacturer based on mic serial number. As long as you zipp them and upload it shouldn't and much as I remember even default graph is psy presentation.

 

[johnsen88]

First: please wear hearing protection, the noises are nasty for the hearing as they focus ALL THE ENERGY to a few hearing cells.

You're going to face two problems basically.

- Are the drivers really damaged?
Look out for the "distortion" tab in REW. The graphs you presented do not show.

- Are the new drivers working properly?
Compare frequency response old versus new. If there's a dip around 2kHz the polarity +/- wire is flipped (don't worry, happens all the time, I stll get nervous after many years of tinkering, it's costly stuff).


That comes later, I suggest to repair first, right?

Yes sir! I will.

"Look out for the "distortion" tab in REW. The graphs you presented do not show."

Here you go.

"Compare frequency response old versus new."

Noted. I will bear this in mind. Glad that you brought this up. Thank you!

 

[Pareto Pragmatic]

Do you want to measure the in-room frequency response?
Then use MMM at your main listening position:

Very true.

But it might be better to start with single position measures, play with those a bit for speaker placement and such, then move to MMM. If for no other reason than it will save a lot of time when figuring out the basics, then the MMM method can be used for final tuning.

Chances are mistakes will be made in early measurements, so entire sets of measurements can be off. Guess how I know?

 

[Heinrich]

Yes sir! I will.

Distortion should look like this, if display is chosen as percentage (hover the mouse left top of values window)



The frequency response is 'normalized' automatically, hence the straight line. Or as absolute dB rel full scale



That colored curves. Sorry, it was done in a hurry, my laptop mike, just for showing.

Play a little with the range, left sidebar.